Abstract
Odour emission from intensive pig production is a major source of local nuisance and sulphur-containing odorants (e.g. hydrogen sulphide and methanethiol) have been recognized as key odorants. Biological air filter has emerged as a cost-effective technique to remove odorants from ventilation air. However, low removal efficiencies for sulphurous odorants have been observed when a large volume of air has been applied with low concentrations. Recent kinetic studies on full scale biological air filters indicate that the removal of odorants is related both to mass load and air load of odorants but the dependence of sulphurous odorants on loading rates are not clear due to the very low and highly varying removal efficiencies. In the present study, two inoculated biofilter columns were applied to test the dependence of sulphurous odorants (hydrogen sulphide, methanethiol and dimethylsulfide) removal on air loading rate, mass loading rate or concentration. Specially designed commercially available ceramic saddles and cellulose pads were selected as biofilter media for the experimental tests. Whereas the air loading ratevaried from around 10 to 1300 m3 m-3 h-1, the mass loading rate varied from approximately 10 to 500 mgm-3 h-1 for hydrogen sulphide. Concentration levels varied from around 10 to 3000 ppbv for hydrogen sulphide, covering the typical concentration range of H2S emitted from pig facilities. The results indicated that the removal of hydrogen sulphide and methanethiol was closely dependent on air loading rate for both biofilter columns. Whereas the removal of hydrogen sulphide was observed to be also dependent on mass loading rate and concentration for the ceramic saddles packed biofilter column, the removal efficiency of H2S was independent on mass loading rate or concentration for cellulose packed biofilter column. Further, significant competition between methanethiol and hydrogen sulphide was observed for the ceramic packed biofilter column, when the mass load of hydrogen sulphide was increased. On the other hand, no such competition was observed for the cellulose packed column. Kinetics analysis indicated that both Grau second-order kinetics and Stover-Kincannon model can generally be applied to describe the degradation of both hydrogen sulphide and methanethiol in biofilters, except a small deviation observed for methanethiol, when applied to Stover-Kincannon model.
